Process for producing benzene and cyclohexane



Oct. 12, 1965 w. L. HOUSTON, JR 3,211,797

PROCESS FOR PRODUCING BENZENE AND GYCLOHEXANE Filed Deo. 22. 1961 W. L. HOUSTON, JR.

Byvf

A TTORNEKS reaction.

United States Patent() 3,211,797 PROCESS FOR PRODUCING BENZENE AND CYCLOHEXANE William L. Houston, Jr., Sweeny, Tex., assigner to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 22, 1961, Ser. No. 161,517 5 Claims. (Cl. 260-668) This invention relates to the production of benzene and of cyclohexane. In one aspect it relates to apparatus and one mode of its operation for the production of a maximum yield of ybenzene from a suitable charge or feed stock and to another mode of operation of the same apparatus for the production of a maximum yield of cyclohexane from the same charge or feed stock. In another aspect it relates to methods of operation of the aforementioned apparatus for the production of maximum yields of either benzene or cyclohexane by regulating the processing flow of methylcyclopentane.

An object of this invention is to provide apparatus and methods for production of cyclohexane and of benzene. Another object of this invention is to provide apparatus which can be used for production of maximum yield of benzene and for maximum yield of cyclohexane. Yet another object of this invention is to provide a given apparatus which can be used for production of maximum yield of benzene and for maximum yield of cyclohexane merely by variations in operating conditions. Still other objects and advantages of this invention will be realized by reading the following description which, taken with the attached drawing, yforms a part of this specification.

The drawing illustrates an arrangement of apparatus parts suitable for use in the production of benzene and of cyclohexane according to this invention.

This invention involves use of a catalytic hydrogenation step and of a catalytic isomerization step along with a catalytic reforming step. As is known in this art, the `reaction of cyclohexane to benzene is a reversible reaction 'and also cyclohexane to methylcyclopentane is a reversible Naturally occurring cyclohexane in the feed stock to the hydrogenation-isomerization portions of this system must be removed to obtain maximum yield of `cyclohexane in the isomerization step. This removed material is charged to the reforming portion of the system in which it is converted to benzene and to methylcyclopentane. When it is desired to produce benzene in maximum yield this methylcyclopentane in relatively large proportions is charged to the feed to the reforming step so thatit will retard 'formation of methylcyclopentane from cyclohexane in the reforming step. When the system is used for the production of cyclohexane only a minimum amount of methylcyclopentane is charged to the reforming -step While the major portion of this methylcyclopenvtane-is passed-to the benzene `hydrogenation step and the `methyl cyclopentane isomerization step. .In this manner alarger amount of methylcyclopentane will be isomerized to .yield more cyclohexane.

When operating for maximum cyclohexane production,

-the-methylcyclopentane content in the tower bottoms from 'the demethylcyclopentanizer is maintained at a minimum, resulting in maximum conversion of cyclohexane to methylcyclopentane in the reforming zone. The methylcyclopentane formed in this reforming step is recovered from the reformate by fractionation, or'by solvent extraction,

.if desired. This .produced methylcyclopentane is then 'charged to the benzene hydrogenaton-methyl cyclopentane .isomerization zones for conversion to cyclohexane. In

-this hydrogenation-isomerization operation the benzene inthe feed s-hydrogenated to Vcyclohexane and the methylcyclopentane is converted to cyclohexane.

For maximum production of benzene, the feed to the reforming step contains a relatively large fraction of 3,211,797 Patented Oct. 12, 1965 methylcyclopentane formed lin the reforming step as Vrecycle material. This addition of methylcyclopentane-suppresses conversion of cyclohexane fto methylcyclopentane `and simultaneously increases `the conversion of cyclohexane to benzene. The concentration ofthe methylcyclopentane in the feed tothe reforming step is `increased by increasing the amount of methylcyclopentane in lthe bottoms from the demethylcyclopentanizer tower. This injected methylcyclopentane is `ultimately recovered and chargedto the methylcyclopentane #isomerization zone by way of the benzene hydrogenation'zone.

The feed stock suitable for use in this operation con tains butanes, pentanes, `isohexanes, vnormalhexane, vmethylcyclopentane, benzene, cyclohexane, isomeric heptanes and higher boiling materials. IWhen this system is used for the production of a maximum lyield of benzene this feed stock material is fractionated in a fractional-distillation vessel 2 having originated at .a source, not shown, and passed through a conduit 1. In fractional distillation tower 2 a major proportion of the cyclohexaneof the'feed is taken overhead while a vminor proportionfor rejection of heptanes passes from this tower-through conduits 26 and 27. Theoverhead cyclohexane passes'through aconduit 3 and is combinedwith a ow of material to be subsequently described and the combined stream :passes on through conduit 4 into a deisohexanizing tower 5. 'The isomeric hexanes of the feed Amaterial from conduit 4 pass overhead in a conduit 9 while the entire cyclohexane content of the feed leaves this tower through a conduit 6. In

another operation a stream containing about cycloconduit 8 to the material flowing vthrough conduit 6 and this combined material passes on through a conduit "7 into a dernethylcyclopentanizer tower 10. When it :is desired to minimize production of benzene the 85% cyclohexane will not normally be added via conduits `8, 55 and valve 55. Fractionator y10 is Aoperated in such a manner as to yield a substantial proportion of the methylcyclopentane into the bottoms passing therefrom by way of a conduit 12. The material passing from tower `10 through conduit 12 is added to the vbottoms from column 2 passing through a conduit 26 and the combined'stream passes on through a conduit 27 to a catalytic reforming unit 31. A-stream of recycle free hydrogengas from a conduit 38 is added to the stream flowing through conduit 27 prior to its introduction to the reforming unit. In this reforming unit numerous chemical reactions take place. Such reactions as dehydrogenation of cyclohexane to benzene, production of methylcyclopentane from cyclohexane, dehydrogenation and cyclization of certain components and hydrogenation of certain components take place. The reforming unit effluent material passes therefrom and is cooled in heat exchangers or coolers 33, 34 or other meansof cooling and'is passed into .a separator vessel 35. In this vessel a hydrogen-rich gas iis-separated and this gas passes through the aforementioned conduit'38for recycling to the reforming zone. Excess -hydrogen not required in this operation is withdrawn 4from the system `4by Way of a conduit 39 for use as fuel or other -use as desired.

Liquid phase reformate separated in separator 35 is lpassed through a conduit 40 to a reformate depentanizer .through a conduit 45 and this material is a benzene-rich material but contains various proportions of other hydrocarbons. This material actually contains a relatively high concentration of methylcyclopentane. This light reformate overhead material from column 44 is passed through conduit 4S to preferably a benzene extraction unit 47 in which a benzene-rich fraction is separated and withdrawn through a conduit 49. The reject from this extraction unit or rainate is passed from unit 47 by way of a conduit 48 and is passed into a raffinate splitter column 50 in which a methylcyclopentane-rich overhead product is taken and passed through a conduit 51 to be added to the overhead from the original preliminary fractionator 2 passing through conduit 3. The bottoms material from rainate spliter 50 leaves this column by way of a conduit 52 for use in motor fuel, or for such processing as desired.

The cyclohexane-lean overhead stream from the distillation tower passing through a conduit 11 contains the benzene from the original feed stock and a relatively high concentration of methylcyclopentane. This material passing through conduit 11 is combined with a recycle material from a conduit 14 to be mentioned hereinafter and the combined stream passes on through a conduit 12a into a benzene hydrogenation unit 13. In this unit the benzene is hydrogenated with the production of cyclohexane. The effluent from this hydrogenation unit is passed on through a conduit 1S into an isomerization unit 16 in which the methylcyclopentane content thereof is largely converted to cyclohexane. The eluent from this isomerization unit then flows through a conduit 17 in a demethylcyclopentanizer tower 18 in which substantially all of the unconverted methylcyclopentane is taken overhead and passed to a methylcyclopentane concentrating fractionating tower 21. In this concentrating tower isomeric hexanes, normal hexane and some methylcyclopentane are taken overhead via conduit 22 while the bottoms material therefrom passes through conduit 14. This bottoms material contains a very appreciable concentration of the methylcyclopentane. The methylcyclopentane-containing stream in conduit 22 can be passed to a concentrator in which this hydrocarbon can be concentrated prior to reuse. The bottoms material from fractionator 18 is removed therefrom and is passed through a conduit to a decyclohexanizer tower 23 in which material is taken overhead in conduit 24 as one of the products of the operation while heavy ends are withdrawn as kettle product by way of a conduit 25. This cyclohexane product is withdrawn from column 23 and passed through a conduit 24 for such use or disposal as desired.

The aforementioned approximately concentration cyclohexane added to the aforedescribed system through conduit 8 is added to the stream flowing from conduit 6 to conduit 7 for de-aeration and drying purposes. In case this 85% cyclohexane is air free and dry it can be added to the system by closing valve 54 and opening valve 55' for addition to the bottoms material from fractionator 10 passing through conduit 12.

This operation just described is the operation in which a maximum benzene product is produced with `a lesser than maximum production of cyclohexane. As an example of the operation of the system Table I includes component stream compositions in various conduits of the apparatus illustrated in the ligure.

While the yield of benzene in this operation is relatively high its purity is not particularly high and it may be preferable to purify the benzene product flowing through conduit 49 by any suitable method for such a degree of purity as required for any particular use. However, the cyclohexane flowing from fractionator 23 through conduit 24 has a purity of approximately 98.6%.

In the operation of the apparatus for the production of cyclohexane in maximum yield with the resultant production of benzene in less than maximum yield, the main points of difference are the distillation column 10 herein termed the demethylcyclopentanizer tower is so operated to allow a larger proportion of the methylcyclopentane to pass overhead through conduit 11 and a lesser proportion to pass through conduits 12 and 27 to the reforming zone. In this manner less methylcyclopentane is present in the cyclohexane feed to the reforming zone with the result that a larger proportion of the cyclohexane of this feed is reformed into the form of methylcyclopentane. When more of the cyclohexane is yielded into methylcyclopentane, then less of the cyclohexane is available for conversion to benzene. Thus while actually a lower concentration of methylcyclopentane is in the intermediate product stream flowing through conduit 51 in the operation for the production of cyclohexane than in the operation for the production of benzene yet a much larger proportion of this methylcyclopentane and of the methylcyclopentane in the original charge stock to the operation is taken overhead from column 10 and -passed directly to the benzene hydrogenation unit 13 and the isomerization unit 16.

TABLE I Maximum benzene Stream No. Component, B/D

"98.6% Purity.

Thus by increasing markedly the flowof methylcyclopentane `from tower through conduit 11 this larger amount of methylcyclopentane yields a relatively larger amount of cyclohexane in the isomerization unit 16. The general operation of the demethylcyclopentanizer tower 18, methylcyclopentane concentrator 21 and the decyclohexanizer tower 23 operated in approximately lthe same manner as described hereinabove Arelative .to the other operation of the system.

As an'illustration of the operation of this system for the production of maximum `yield of cyclohexane are the data given 'in VTable 2.

,6 .one s pecificoperation the hydrogen to hydrocarbon mol ratios used varied within a range of about 6 to 1 to 7 to 1. In this case the liquid hourly space velocity `(barrels per hour of hydrocarbon charge per barrel of catalyst) Varied from about 2.3 to about 3.0. The 'temperature maintained in the reactor or reactors, as the case may be, are preferably Within the range of about 800 to about 900 F., with pressures varying from about 500 to about 800 p.s.i.g. If desired, however, a single reactor vessel can be used but it is preferable to employ multiple reactors such as two or three reactors. In case three reactors are used, temperature in the rst reactor of this system TABLE II Maximum cyclohexane Stream No. Component, B/D

12 12 12 v 37 5 42 42 Y l 1, 633 245 1, 878 180 1, 698 180 v180 20 200 200 2, 930 114 3, 050 2,150 Y 900 2,150 2,150 305 2, 515 2, 515 1, 247 542 1, 789 1, 709 80 4 1, 713 1, 599 114 442 2, 041 2, 041 T385 .3 388 323 3 323 `323 797 4 801 801 840 1, 641 50 1, 591 60 110 504 453 37 490 484 6 106 590 20 570 20 20 7,500 950 s, 450 5, 047 2, 803 950 n e, 597 4, 322 2, 275 p 887 5, 209 5, 280

1,177 1, 141 35 1, 13s v 00 1, 80s 44 44 40 1, 72s 20 2, 010 419 00 8, 805 1, 001 7, 264 1, 177 20 40 10, 070 v 387 9, 500

*98.3% Purity.

The several-fractional distillation towers illustrated in the drawing land mentioned vhereinbefore are `provided with suitable vapor-liquid contact promoting apparatus such as bubblecaptrays or the like.

The benzene fhydrogenation unit 13 can be any suitable type of benzene hydrogenation ,unit as long as it serves-its intended purpose. However such a hydrogenation system is fully described in U.S. Patent 2,906,784, issued September 29, 1959. The catalyst used in this particular hydrogenation system is nickel on kieselguhr, the nickel content ranging from about 20 to about 55 weight percent of the catalyst. A preferable temperature range -for operation of this benzene hydrogenation step is from about 370 to about 500 F. with pressures ranging from approximately 400 to about 500 p.s.i.g. (pounds per square inch gauge). The hydrogen to aromatic cornpounds mol ratios are in the range of about 5 to 1 to 12 to 1.

In the isomerization step which can, if desired, employ an aluminum chloride isomerization catalyst, the isomerization is effected at a temperature within the range of about to 170 F., and preferably from about 100 to F. Pressures used are generally within the range of about to 200 p.s.i.g. preferably from about 170 to p.s.i.g. The catalyst used is an aluminum chloride complex promoted by hydrochloric acid, such catalyst and its use being described in U.S. Patent No. 2,999,890.

The reforming step of this operation can be such a reforming step as described in U.S. Patent 2,985,583, issued May 23, 1961. The catalyst employed in this reforming operation is a platinum-containing catalyst and its method of preparation is described in U.S. Patent 2,479,109, issued August 16, 1949. In this reforming operation the amount of hydrogen cycled thereto can vary within rather wide limits, for example, from about 5 to about 9 mols of hydrogen per mol of charge stock. In

is maintained at about 910 `to 915 F.,'with pressure of about 325 to 330 p.s.i.g. In the second reactor temperatures can vary from about 915 to about 920 F. at pressures of about 320 to 325 p.s.i.g. In the third reactor the temperature is varied from about 915 to 925 F. at pressures of about 315 to 320 p.s.i.g. As is Well known in the art, there is an appreciable temperature drop through such reforming reactors and that is the reason a heater is required just prior to entry of feed into each of the three reactors. The effluent from the first reactor had a .temperature of about 770 to about 785 F., from the second reactor it was about 825 to 835 F. and the final reactor was about 865 to 885 F. The separator vessel 35 was maintained at about 85 F. at 280 p.s.i.g.

The benzene extractor 47 can be any suitable extraction or fractionation system as long as it is adapted for the separation of benzene from non-aromatic hydrocarbons. In one instance a Udex extraction system was employed. This system employs solvent of glycol and Water for the separation of aromatics from mixtures with other hydrocarbons. A description of this system and its broad operation is found in the September, 1952, issue of Petroleum Refiner, page 82.

This extraction lprocess is also described in Petroleum Refiner for June, 1959, pages 161 to 164.

While certain embodiments of the invention have been described for illustrative purposes, the invention obviously is not limited thereto.

I claim:

1. A method for producing cyclohexane from a first feed stream containing methylcyclopentane, benzene, and hexanes including cyclohexane and a second feed stream containing a major amount of methylcyclopentane and minor amounts of hexanes comprising the steps of z (a) separating from these feed streams in a first fractionation step a rst fraction containing the major portions of the methylcyclopentane, benzene and cyclohexane;

(b) separating this rst fraction in a second fractionation step into a second fraction containing the major portion of the cyclohexane and a minor portion of the methylcyclopentane of said iirst fraction and a third fraction containing the major portions of the methylcyclopentane and the benzene of the irst fraction;

(c) catalytically reforming said second fraction in the presence of added hydrogen gas to form benzene; (d) separating the eiiiuent of the reforming step into a hydrogen gas phase and a reformate phase rich in benzene, this gas phase comprising said added hydrogen gas;

(e) from the reformate phase separating benzene as a first product of the operation and separating an additional fraction rich in methylcyclopentane, said additional fraction comprising the aforesaid second feed stream;

(f) hydrogenating said third fraction thereby converting benzene therein into cyclohexane;

(g) `isomerizing the effluent of this latter hydrogenating step thereby converting methylcyclopentane into cyclohexane;

(h) from the eluent of this isomerizing step separating a fraction rich in cyclohexane as a second product of the operation;

(i) for a substantial period of time, increasing the yield of cyclohexane by operating said second fractionation step so as to decrease the concentration of methylcyclopentane in said second fraction; and

(j) for another substantial period of time, increasing the yield of benzene by operating said second fractionation step so as to increase the concentration of methylcyclopentane in said second fraction.

2. A iieXible process for producing benzene and cyclohexane in variable yields from a feed stock rich in methylcyclopentane and cyclohexane and containing a minor concentration of benzene, which comprises the steps of:

(a) distilling said feed stock so as to produce an overhead stream rich in methylcyclopentane and containing a minor concentration of benzene and a bottoms stream rich in cyclohexane and containing a minor concentration of methylcyclopentane;

(b) catalytically hydrogenating the overhead stream of 8 step (a) in admixture with H2 so as to convert said benzene therein to cyclohexane;

(c) catalytically `isomerizing the hydrogenated eluent of step (b) so as to convert the methylcyclopentane therein to cyclohexane;

(d) recovering a cyclohexane-rich stream from the eiuent step (c) as a product of the process;

(e) catalytically reforming the bottoms stream of step (a) in admixture with H2 to convert cyclohexane and methylcyclopentane to benzene;

(f) recovering a benzene-rich stream from the effluent of step (e) as another product of the process;

(g) for a substantial period, operating distilling step (a) so as to provide a relatively low methylcyclopentane concentration in the bottoms stream and increase its concentration in the overhead stream to produce a relatively high yield of cyclohexane; and

(h) for another substantial period, operating distilling step (a) so as to provide a relatively high methylcyclopentane concentration in the bottoms stream and decrease its concentration in the overhead stream to produce a relatively high yield of benzene.

3. The process of claim 2 including the steps of (i) recovering a methylcyclopentane-rich stream from the effluent of step (e); and

(j) feeding the recovered stream of step (i) to step (a).

4. The process of claim 2 wherein the catalyst in step (c) comprises aluminum chloride and the catalyst of step (e) comprises platinum.

5. The process of claim 2 including the step of adding a stream of hydrocarbons containing about weight percent of cyclohexane along with said first bottoms to the catalytic reforming step to increase the yield of benzene.

References Cited by the Examiner UNITED STATES PATENTS 2,373,501 4/45 Peterson 260-667 2,373,673 4/45 Fuller et al. 260-667 X 2,626,893 1/53 Morrow 260-668 2,718,535 9/55 McKinley et al 260-666 2,911,451 11/59 Haensel 260-668 3,117,096 1/64 Harris et al. 260-668 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A METHOD FOR PRODUCING CYCLOHEXANE FROM A FIRST FEED STREAM CONTAINING METHYLCYCLOPENTANE, BENZENE, AND HEXANES INCLUDING CYCLOHEXANE AND A SECOND FEED STREAM CONTAINING A MAJOR AMOUNT OF METHYLCYCLOPENTANE AND MINOR AMOUNTS OF HEXANES COMPRISING THE STEPS OF: (A) SEPARATING FROM THESE FEED STREAMS IN A FIRST FRACTIONATION STEP A FIRST FRACTION CONTAINING THE MAJOR PORTIONS OF THE METHYLCYCLOPENTANE, BENZENE AND CYCLOHEXANE; (B) SEPARATING THIS FIRST FRACTION IN A SECOND FRACTIONATION STEP INTO A SECOND FRACTION CONTAINING THE MAJOR PORTION OF THE CYCLOHEXANE AND A MINOR PORTION OF THE METHYLCYCLOPENTANE OF SAID FIRST FRACTION AND A THIRD FRACTION CONTAINING THE MAJOR PORTIONS OF THE METHYLCYCLOPENTANE AND THE BENZENE OF THE FIRST FRACTION; (C) CATALYTICALLY REFORMING SAID SECOND FRACTION IN THE PRESENCE OF ADDED GAS TO FORM BENZENE; (D) SEPARATING THE EFFLUENT OF THE REFORMING STEP INTO A HYDROGEN GAS PHASE AND A REFORMATE PHASE RICH IN BENZENE, THIS GAS PHASE COMPRISING SAID ADDED HYDROGEN GAS; (E) FROM THE REFORMATE PHASE SEPARATING BENZENE AS A FIRST PRODUCT OF THE OPERATION AND SEPARATING AN ADDITIONAL FRACTION RICH IN METHYLCYCLOPENTANE, SAID ADDITIONAL FRACTION COMPRISING THE AFORESAID SECOND FEED STREAM; (F) HYDROGENATING SAID THIRD FRACTION THEREBY CONVERTING BENZENE THEREIN INTO CYCLOHEXANE; (G) ISOMERIZING THE EFFLUENT OF THIS LATTER HYDROGENATING STEP THEREBY CONVERTING METHYLCYCLOPENTANE INTO CYCLOHEXANE; (H) FROM THE EFFLUENT OF THIS ISOMERIZING STEP SEPARATING A FRACTION RICH IN CYCLOHEXANE AS A SECOND PRODUCT OF THE OPERATION; (I) FOR A SUBSTANTIAL PERIOD OF TIME, INCREASING THE YIELD OF CYCLOHEXANE BY OPERATING SAID SECOND FRACTIONATION STEP SO AS TO DECREASE THE CONCENTRATION OF METHYLCYCLOPENTANE IN SAID SECOND FRACTION; AND (J) FOR ANOTHER SUBSTANTIAL PERIOD OF TIME, INCREASING THE YIELD OF BENZENE BY OPERATING SAID SECOND FRACTIONATION STEP SO AS TO INCREASE THE CONCENTRATION OF METHYLCYCLOPENTANE IN SAID SECOND FRACTION. 